20 HP Honda Longtail HP increase

[PaulC]

I have a 20 hp honda longtail that is just a hair underpowered for my rig. I was wondering if anyone on here knew how a 20 HP honda GX620 can be tweaked to get a few more HP?

I am thinking that the difference betwen the 20 and 24 hp honda engines may be Carbs and intake manifold?

Thanks

[FastDuck]

They are tempramental. What RPM's are you turning out of the water? You should be around 4100 out of the water at full throttle. Do you have a Tach on it?

[novaalex]

Be very careful. My partner and I had two of those motors. Motor 1: Defective from Factory blew up less than 15 hours and had to be totally rebuilt. Motor 2: Very reliable for 3 years but started acting up after that and I had to replace lifters because they have to be adjusted after spark plug changes and I didnt do that. I would be very careful modifying one of those!

[FastDuck]

Paul do you have a tach on it?

[PaulC]

Sorry for the delay, no i don't have a tach on it.

I ran it last year fine, just oil changes but even though I thought i ran all the gas out if last year some must have stayed in it as now the carb is acting up. So I figured if I have to take the carb off and rebuild it I might as well see if I could get a few xtra HP out of it. I was thinking because the 24 hp has the same bore stroke etc that perhaps a carb and manifold change might be worth investigating.

Basically with a full tank and one of my larger friends I cannot get it onto a plane. If I have smaller guy a little less gas then full I can get on a plane and scoot along nicely. The boat has the beavertail pods on it already

[FastDuck]

I don't think the manifolds match up on the block but it never hurts to see if they do. You probably don't need to rebuild the carb but clean it real good and you should be fine. run some carb cleaner and pull the jets out of it and clean those really good you should be back in business. If you can pick up a tach for it and check the rpms your cable could have slipped or something could have happened there as well. If you think it is a carb I would start there first then check the rpms.

[SSPhone]

You may want to post over at www.mudmotortalk.com, you may find someone else that has done the same as you are looking to do. Or if you want to make HP you may want to look at www.mudboatmotor.com Sheldon can make HP for you :toothy10:

[PaulC]

Thanks alot for the reply's guys.

I finally have the carb cleaned out and back together and purring. Anyways I got a tach and bumped the RPMS up from 3700 to 4100 so will go run it this weekend and see how it does with the extra 400 turns. Hopefully I will be able to find a few birds while I'm at it.

[FastDuck]

Glad to hear you got it going. The tach is a huge help and a great indicator for getting the most out of your motor.